Electrohydraulic servo valves (EHSVs) may be used in myriad systems and environments. One typical system and environment is the fuel control system on-board a jet-powered aircraft. No matter the specific end-use system and environment, EHSVs typically include a pair of nozzles that are coupled between a pressurized hydraulic fluid source and a hydraulically controlled load. Pressurized hydraulic fluid flow through each of the nozzles, and thus to the hydraulically controlled load, may be controlled via a torque motor.
A typical torque motor that is used with an EHSV includes a plurality of coils, an armature, and a flapper. The coils are controllably energized to control the rotational position of the armature. The flapper is coupled to the armature and extends between the outlets of each of the nozzles in the EHSV. By controlling the rotational position of the armature, the position of the flapper relative to each of the nozzle outlets is controlled, and thus fluid pressure and/or flow to the hydraulically controlled device is controlled.
The flapper in the above-described torque motor extends into the flow of hydraulic fluid. Thus, to protect the electrically energized portions of the torque motor from the hydraulic fluid, a suitable liquid-to-air seal is employed. Such seals, in the past, have typically been embodied as elastomeric packing, such as an O-ring. While these seals are generally safe, reliable, and robust, these seals may suffer certain drawbacks. For example, the use of an O-ring may limit both the lower and upper operational temperature limits for the EHSV. Further, the O-ring may also create hysteresis in valve operation, which may lead to a dead band and null shift.
Hence, there is a need for an improved seal for a torque motor that is used with an EHSV. In particular, there is a need for a seal that is able to operate in a wider range of temperatures, and is less susceptible to creating hysteresis in valve operation, as compared to presently known seals. It would also be beneficial to reduce assembly time of the EHSV. The present disclosure addresses at least these needs.